C = 1 + 21 + 22 + 23 + ... + 22018
2C = 21 + 22 + 23 + ... + 22018 + 22019
2C - C = C = ( 21 + 22 + 23 + ... + 22018 + 22019) - ( 1 + 21 + 22 + 23 + ... + 22018 )
C = 22019 - 1
\(C=1+2^1+2^2+2^3+2^4+.....+2^{2018}\)
\(\Leftrightarrow2C=2+2^3+2^4+2^5+....+2^{2019}\)
\(\Leftrightarrow2C-C=\left(2+2^{2019}\right)-\left(1+2^2\right)\)
\(\Leftrightarrow C=2+2^{2019}-2-2^2\)
\(\Leftrightarrow C=2+2^{2019}-5\)
\(\Leftrightarrow C=2^{2019}-3\)
Vậy : \(A=2^{2019}-3\)